Resolving a PEM Fuel Cell Dichotomy: Maximum-Power-Point or Maximum-Efficiency-Point Tracking?

Performance metrics for maximum-power-point tracking (MPPT) and maximum-efficiency-point tracking (MEPT) strategies for the management of open-cathode direct methanol fuel cells are characterized via simulation studies. The liquid saturation level is invoked for the novel role of serving as a performance metric that diagnoses potential failures. MPPT improves the fuel efficiency of the device; however, it suffers from significant disadvantages, including (i) lowering the voltage efficiency and thus the quality of electrical work, (ii) making the device vulnerable to failure by falling to a zero-voltage operating point under small perturbations, and (iii) driving the device perilously close to failure points due to the high production of water leading to saturation levels in excess of 90 % inside the pores of the liquid distribution layer used for oxygen molecules to reach the cathode reaction sites. In contrast, MEPT leads to (i) improvements in the real efficiency of the fuel cell by 18 %, (ii) safer operation away from limiting currents, (iii) better voltage efficiency, and (iv) maintaining an adequate liquid saturation level of 52 % for water in the pores leading to a significant mitigation of the risk of failure caused by cathode dry-out or flooding conditions.